1. Field of the Invention
The invention relates to a travel guiding apparatus for a vehicle and a travel guiding method for a vehicle, which determine the type of a road on which a vehicle is traveling, and a computer-readable storage medium that stores computer-executable instructions for performing the method.
2. Description of the Related Art
Recently, vehicles have been provided with navigation apparatuses that provide guidance regarding the travel of the vehicles so that drivers easily reach desired destinations. In the navigation apparatus, the current position of the vehicle is detected using a GPS receiver or the like, map information regarding the current position is acquired through a storage medium such as a DVD-ROM or a HDD, or through a network, and a map image regarding an area around the vehicle is displayed on a liquid crystal monitor. Further, a road on which the vehicle is currently traveling (hereinafter, the road on which the vehicle is traveling may be referred to as “a vehicle traveling road”) is indicated on the displayed map image. When the vehicle traveling road is determined based on the current position of the vehicle and the map information, the vehicle traveling road may not be accurately determined.
That is, when the vehicle is traveling in a region in which an elevated expressway is located above an ordinary road or an elevated ordinary road is located above an expressway, or an expressway extends in parallel with an ordinary road, the navigation apparatus cannot accurately determine on which of the expressway and the ordinary road the vehicle is traveling. As a result, the navigation apparatus may determine and indicate that the vehicle is currently traveling on a road that is different from a road on which the vehicle is actually traveling. Thus, Japanese Patent Application Publication No. 2001-289651 (JP-A-2001-289651) (refer to pages 5 and 6 and FIG. 3) describes a navigation apparatus including a camera that captures the image of the surface of a vehicle traveling road. In the navigation apparatus, the length of a white-line interval relating to white lines included in a lane marking on the vehicle traveling road is measured based on the image captured by the camera. One lane marking is composed of a plurality of white lines. The white-line interval is a distance from the starting end of one white line to the starting end of another white line. Then, it is determined whether the vehicle traveling road is an expressway or an ordinary road, based on the measured length of the white-line interval.